A prefilled syringe in which a liquid medicine is filled in advance has been conventionally used to prevent use of a mix-up of medicine, prevent hospital infection, disposability, and increase efficiency in hospital service. A syringe including a syringe to be used as the prefilled syringe can be constructed of an outer cylinder, a gasket slidable inside the syringe, and a plunger for operating the movement of the gasket. To enhance the sliding performance of the gasket and obtain a high degree of flow accuracy without generating a large irregularity in the discharge of the liquid medicine, silicone oil or the like is applied to a sliding portion of the outer surface of the gasket or the inner surface of the syringe as a lubricant. Depending on the kind of a liquid medicine that is used, an interaction can occur between the liquid medicine and the lubricant such as the silicone oil. When the liquid medicine is stored for a long time after the liquid medicine is filled in the syringe, the liquid medicine can be denatured by the interaction. Thus, it is difficult to use some kinds of medicines with a prefilled syringe.
The prefilled syringe to be stored for a long time with the liquid medicine filled therein can be beneficial for keeping the liquid medicine stable and eliminate the need for the lubricant.
To solve the above-described problem, as disclosed in a patent document 1 (Japanese Patent Publication Laid-Open No. 62-32970) and a patent document 2 (Japanese Patent Publication Laid-Open No. 2002-089717, U.S. Pat. No. 7,111,848), prefilled syringes were proposed in which the surface of the gasket is covered with the fluorine resin which is a material having a lower friction coefficient than the material of the gasket body to eliminate the use of the lubricant.
The present applicant proposed the gasket having the coating layer composed of the fluorine resin, the silicon resin, and the urethane resin, as disclosed in a patent document 3 (Japanese Patent Publication Laid-Open No. 2004-321614); and the gasket having the coating layer composed of the film made of the composition containing the sliding property-imparting component and the flexibility-imparting component and of the fine particles held by the film to form the rough surface on the gasket, as disclosed in a patent document 4 (Japanese Patent Publication Laid-Open No. 2006-167110).
Patent document 1: Japanese Patent Publication Laid-Open No. 62-32970
Patent document 2: Japanese Patent Publication Laid-Open No. 2002-089717, U.S. Pat. No. 7,111,848
Patent document 3: Japanese Patent Publication Laid-Open No. 2004-321614
Patent document 4: Japanese Patent Publication Laid-Open No. 2006-167110
The gaskets disclosed in the patent document 1 (Japanese Patent Publication Laid-Open No. 62-32970) and the patent document 2 (Japanese Patent Publication Laid-Open No. 2002-089717, U.S. Pat. No. 7,111,848) are expected to be effective in dependence on a use condition. But in a preparation for a prefilled syringe demanded to discharge the liquid medicine under a high pressure and have the performance of stably discharging the liquid medicine little by little with a very high accuracy for a long time by using a syringe pump or the like, liquid-tightness and sliding performance which are fundamental performance demanded for the syringe are still in a trade-off relationship. A syringe which allows these performances to be compatible with each other at a high level and has a higher performance is needed.
That is, in administration of the liquid medicine by using the syringe pump, when the liquid medicine is discharged in a condition where the flow rate is so low that the flow of the liquid medicine is invisible (for example, in the syringe having a diameter of about 24 mm, a moving speed of a gasket when it is made to discharge in 1 mL/hour is about 2 mm/hour), an unstable discharge state called pulsation is liable to occur. Thus there is a fear that accurate administration of the liquid medicine is prevented.
The gaskets disclosed in the patent document 3 (Japanese Patent Publication Laid-Open No. 2004-321614) and the patent document 4 (Japanese Patent Publication Laid-Open No. 2006-167110) are liquid-tight and have stable sliding performance without applying a lubricant to the sliding surface thereof. But in the former, materials forming the coating layer are used in a wide variety and hence the former has problems in terms of production and cost. The latter has a problem that fine particles held by the coating layer cause the formation of the coating layer to be difficult.